Single tooth restorations present the unique requirement that they must be supported non-rotationally on the underlying abutment. When a prepared natural tooth is the underlying abutment, this requirement is met in the normal course of preparing the abutment with a non-circular cross-section. Likewise, when the underlying abutment is a post fitted onto an implant, this requirement is met by preparing the post with a noncircular cross-section. This latter scenario can be more complicated due to the added connection between the implant and the abutment.
Typically, a dental implant is implanted into the bone of a patient's jaw and comprises a socket, e.g., a bore, which is accessible through the overlying or surrounding gum tissue for receiving and supporting one or more attachments or components which, in turn, are useful to fabricate and support the prosthodontic restoration. Dental implant procedures can use a variety of implanting modalities, for example, blade, threaded implant, or smooth push-in implant. The present invention is not concerned with the implant modality that is used. The invention is, however, concerned with connections between implants and attachments, as well as with other matters.
With respect to connections used in implant systems, internal threads of the implant have been used to connect abutments having threaded stems. Rotational alignment is not, however, easily achieved using threaded connections. Further, such a threaded bore, by itself, cannot generally provide rotational fixing. Rotationally fixing the prosthetic tooth to the abutment, and rotationally fixing the abutment to the implant, must be accomplished to ensure that the prosthetic tooth is non-rotational in the mouth of the patient after the restoration process is complete. To improve the likelihood that the implant will not exhibit movement, the implant is typically allowed to undergo osseointegration prior to being subjected to normal loading.
To overcome the non-rotational deficiency between the implant and attachments, dental implants include an anti-rotational structure to restrain components attached to the implant against rotation relative to the implant around the longitudinal axis through the bore. A common structure used to restrain rotation includes a male projection or a female indentation located on or near the gingival surface of the implant which is concentric with the opening into the bore. These designs are not, however, free of problems.
An inherent disadvantage of implant components is that their small size makes assembly difficult. Problems include the difficulty of properly positioning abutments in implants. The relatively small size of the components and tight working environment make it difficult to know when an abutment is properly seated in an implant. Related problems include abutments becoming loose due to the extreme forces incurred through normal chewing actions. Traditionally, axial retention has been achieved with a screw threading through the abutment and attaching to the implant. More recently, attempts have been made to eliminate the axial screw by using snap-in abutments. These snap-in abutments generally are provided with protrusions extending from the distal end of the stem of the abutment. Some of these snap-in designs are more successful than others. Practitioners have noted that some abutments used in these screwless systems become loose due to the large forces generated through chewing. For some, the disadvantages associated with screwless abutments outweigh any potential benefits.
These screwless abutments also exhibit unacceptable axial movement. This axial movement can lead to damage of the abutment or the implant as a result of misaligned forces and increased internal wear. The internal wear and misaligned forces lead to further unacceptable movement, inevitably requiring repair and replacement. In the mildest cases, the patient is inconvenienced. In the more severe cases, where the patient waits too long, infection and permanent bone and tissue damage occur. Thus, even systems that provide adequate connection must continually be improved upon to reduce patient suffering, or worse.
The prior art has successfully addressed many problems. But not all disadvantages have been overcome, and some solutions carry their own disadvantages.